Graphene pressure sensors

ABSTRACT

Semiconductor nano pressure sensor devices having graphene membrane suspended over open cavities formed in a semiconductor substrate. A suspended graphene membrane serves as an active electro-mechanical membrane for sensing pressure, which can be made very thin, from about one atomic layer to about 10 atomic layers in thickness, to improve the sensitivity and reliability of a semiconductor pressure sensor device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.13/445,029, filed on Apr. 12, 2012, the disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

The field relates generally to semiconductor nano-devices for sensingpressure and, in particular, semiconductor nano-pressure sensor devicesthat are constructed using thin graphene membranes.

BACKGROUND

In general, semiconductor nano pressure sensor devices are used tomeasure the pressure of gases or liquids, for example, and are utilizedin various control and real-time monitoring applications. Semiconductornano pressure sensor devices can also be utilized to indirectly measureother variables such as fluid flow, gas flow, speed, water level, andaltitude, for example. Commonly used pressure sensors implement a straingauge device with an active membrane that is made of silicon(monocrystalline), a polysilicon thin film, a bonded metal foil, a thickfilm, or a sputtered thin film, for example. Typically, the thinner theactive membrane, the more deformation there will be of the membranematerial in response to external pressure, thereby providing highersensitivity and precision. It is very challenging, however, to produceultra-thin silicon membrane for use with a pressure sensor device due tothe brittle nature of the material.

SUMMARY

Aspects of the invention include semiconductor nano-devices for sensingpressure and, in particular, semiconductor nano pressure sensor devicesthat are constructed using thin graphene membranes. A suspended graphenefilm serves as an active electro-mechanical membrane for sensingpressure, which can be made very thin, from about one atomic layer toabout 10 atomic layers in thickness, to greatly improve the sensitivityand reliability of a semiconductor pressure sensor device.

For example, in one aspect of the invention, a semiconductor pressuresensor device includes an insulating layer disposed on a semiconductorsubstrate, wherein a recessed cavity is formed in the insulating layer.A first graphene membrane is disposed on a surface of the insulatinglayer completely covering the recessed cavity. A first sense electrodeand a second sense electrode are disposed on the insulating layer onopposing sides of, and in contact with, the first graphene membrane. Asealing ring forms a seal around outer sidewalls of the first and secondsense electrodes and the first graphene membrane.

In another aspect of the invention, the semiconductor pressure sensordevice further includes a second graphene membrane disposed on a surfaceof the insulating layer in a region adjacent to the first graphenemembrane. A third sense electrode and a fourth sense electrode aredisposed on the insulating layer on opposing sides of, and in contactwith, the second graphene membrane. A second sealing ring forms a sealaround outer sidewalls of the third and fourth sense electrodes and thesecond graphene membrane.

In yet another aspect of the invention, a method of forming asemiconductor pressure sensor device includes forming an insulatinglayer on a semiconductor substrate, forming a recessed cavity in theinsulating layer, forming a first graphene membrane on a surface of theinsulating layer completely covering the recessed cavity, forming afirst sense electrode and a second sense electrode on the insulatinglayer on opposing sides of, and in contact with, the first graphenemembrane, and forming a sealing ring around outer sidewalls of the firstand second sense electrodes and the first graphene membrane.

In another aspect of the invention, the method further includes forminga second graphene membrane on a surface of the insulating layer in aregion adjacent to the first graphene membrane, forming a third senseelectrode and a fourth sense electrode on the insulating layer onopposing sides of, and in contact with, the second graphene membrane;and forming a second sealing ring around outer sidewalls of the thirdand fourth sense electrodes and the second graphene membrane.

These and other aspects, features and embodiments of the presentinvention will become apparent from the following detailed descriptionof preferred embodiments, which is to be read in conjunction with theaccompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top schematic plan view of a semiconductor nano pressuresensor device according to an aspect of the invention.

FIG. 1B is a side schematic view of the semiconductor nano pressuresensor device taken along line 1B-1B in FIG. 1A.

FIG. 1C is a side schematic view of the semiconductor nano pressuresensor device taken along line 1C-1C in FIG. 1A.

FIGS. 2A and 2B schematically illustrate methods for operatingsemiconductor nano pressure sensor device according various aspects ofthe invention.

FIGS. 3A, 3B, 3C, 3D, 3E, and 3F schematically illustrate a method forconstructing a graphene pressure sensor device at various stages offabrication, according to an aspect of the invention, wherein:

FIG. 3A, a cross-sectional view is shown of the semiconductor nanodevice at an initial stage of fabrication after forming an insulatinglayer on a semiconductor substrate,

FIG. 3B is a cross-sectional view of the structure of FIG. 3A afteretching a cavity in the insulating layer,

FIG. 3C is a cross-sectional view of the structure of FIG. 3B afterforming a graphene layer over the insulating layer and forming a secondetch mask over the graphene layer,

FIG. 3D is a cross-sectional view of the structure of FIG. 3C afteretching the graphene layer to form the supported graphene membrane andthe suspended graphene membrane,

FIG. 3E is a cross-sectional view of the structure of FIG. 3D afterforming a layer of conductive material over the graphene membranes andinsulating layer, and forming an etch mask to define sense electrodes,

FIG. 3F is a cross-sectional view of the structure of FIG. 3E afteretching the exposed portions of the layer of conductive material to formthe sense electrodes,

FIG. 3G is a cross-sectional view of the structure of FIG. 3F afterdepositing a blanket layer of sealing material and forming an etch maskthat defines sealing rings to be formed by etching the layer of sealingmaterial.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will now be described in furtherdetail with regard to semiconductor nano pressure sensor devices thatare constructed using thin graphene membranes. For example, FIGS. 1A,1B, and 1C collectively illustrate a semiconductor nano pressure sensordevice 100 according to an aspect of the invention. In particular, FIG.1A is a top schematic plan view of the semiconductor nano pressuresensor device 100, FIG. 1B is a side schematic view of the semiconductornano pressure sensor device 100 taken along line 1B-1B in FIG. 1A, andFIG. 1C is a side schematic view of the semiconductor nano pressuresensor device 100 taken along line 1C-1C in FIG. 1A. Referringcollectively to FIGS. 1A, 1B and 1C, the nano pressure sensor device 100generally comprises a bulk semiconductor substrate 105, an insulatinglayer 110, a recessed cavity 115 formed in the insulating layer 110, afirst graphene membrane 120 (supported membrane), a second graphenemembrane 125 (suspended membrane) that is formed over the recessedcavity 115, sense electrodes 130, 131, 132 and 133, and sealing rings140 and 145.

In general, the graphene membranes 120 and 125 are used to detectpressure of an applied test gas based on changes in resistance of thegraphene membranes 120, 125, as will be discussed in further detailbelow with reference to FIGS. 2A and 2B. As specifically shown in FIG.1A, for example, the graphene membranes 120 and 125 arerectangular-shaped membranes, wherein the sense electrodes 130 and 131are formed in contact with opposing sides of the supported graphenemembrane 120, and the sense electrodes 132 and 133 are formed in contactwith opposing sides of the suspended graphene membrane 125. The senseelectrodes 130 and 131 partially overlap the top surface of thesupported graphene membrane 120 along the edges thereof. Similarly, thesense electrodes 132 and 133 partially overlap the top surface of thesuspended graphene membrane 125 along the edges thereof.

The sense electrodes 130 and 131 are used to apply a control voltageacross the supported graphene membrane 120 and measure its resistancebased on current flowing through the supported graphene membrane 120between the sense electrodes 130 and 131. Similarly, the senseelectrodes 132 and 133 are used to apply a control voltage across thesuspended graphene membrane 125 and measure its resistance based oncurrent flowing through the suspended graphene membrane 125 between thesense electrodes 132 and 133.

As further depicted in FIG. 1A, the sealing ring 140 (which has an inneredge 141) forms a seal around outer sidewalls of the sense electrodes130 and 131 and the supported graphene membrane 120. In addition, thesealing ring 140 partially overlaps the top surface of the supportedgraphene membrane 120 and sense electrodes 130 and 131 along the outersidewalls thereof. In particular, the inner edge 141 of the sealing ring140 is disposed on top of the sense electrodes 130 and 131 and supportedgraphene membrane 120, and extends past three sides of the senseelectrodes 130 and 131, and two opposing sides of the supported graphenemembrane 120. The sealing ring 140 serves to prevent external gases fromleaking underneath the supported graphene membrane 120 from under theside edges of the supported graphene membrane 120 and from under theside edges of the sense electrodes 130 and 131.

Similarly, the sealing ring 145 (which has an inner edge 146) forms aseal around outer sidewalls of the sense electrodes 132 and 133 and thesuspended graphene membrane 125. In addition, the sealing ring 145partially overlaps the top surface of the suspended graphene membrane125 and sense electrodes 132 and 133 along the outer sidewalls thereof.In particular, the inner edge 146 of the sealing ring 145 is disposed ontop of the sense electrodes 132 and 133 and suspended graphene membrane125, and extends past three sides of the sense electrodes 132 and 133,and two opposing sides of the suspended graphene membrane 125. Thesealing layer 145 serves to prevent external gases from leaking into orout of the cavity 115 from under the side edges of the suspendedgraphene membrane 125 and from under the side edges of the senseelectrodes 132 and 133.

Moreover, as shown in FIGS. 1A, 1B and 1C, the suspended graphenemembrane 125 is formed to extend past each of the peripheral surfaceedges of the recessed cavity 115 to completely cover the recessed cavity115. The recessed cavity 115 can be filled with air, or it may be formedto contain a vacuum. The combination of the suspended graphene membrane125, sense electrodes 132, 132 and the sealing ring 145 serve to sealthe air or vacuum within the recessed cavity 115 and prevent any testgases from infiltrating the recessed cavity 115 during use. As shown inFIGS. 1B and 1C, the recessed cavity is formed to a depth D, a width Wand a length L. As specifically shown in FIG. 1B, the depth D of therecessed cavity 115 is preferably in range of about 20 nm to about 300nm. Moreover, as shown in FIGS. 1A and 1B, the width W of the cavity 115(in the direction extending between the sense electrodes 132 and 133) isin a range of about 0.2 um to about 5.0 um, or more preferably fromabout 0.5 um to about 2.0 um. Furthermore, as specifically shown inFIGS. 1A and 1C, the length L of the cavity 115 (in the directionextending along the sense electrodes 132 and 133 is in a range of about0.2 um to about 5.0 um. An exemplary method and materials used forfabricating a semiconductor nano-device 100 as depicted in FIGS. 1A, 1Band 1C, will be discussed in further detail below with reference toFIGS. 3A˜3G.

FIGS. 2A and 2B schematically illustrate methods for operating asemiconductor nano pressure sensor device according various aspects ofthe invention to determine pressure of a test gas. In general, FIGS. 2Aand 2B illustrate the structure shown in FIG. 1B, wherein the portion ofthe device 100 that comprises the suspended graphene membrane 125 isutilized as a device cell 200 and the portion of the device 100 thatcomprises the supported graphene membrane 120 is optionally utilized asa control cell 210. In one exemplary embodiment of the invention, in afirst mode of operation, a method for sensing the pressure of a testambient is performed using only the device cell 200 portion of thepressure sensor device 100 (i.e., the control cell 210 is an optionalstructure). In another exemplary embodiment of the invention, a methodfor sensing the pressure of a test ambient is performed using both thedevice cell 200 and control cell 210 portions of the pressure sensordevice 100.

More specifically, in the first mode of operation, as shown in FIG. 2A,a first step comprises placing the pressure sensor device 100 in areference ambient having a known pressure P_(ref), and then measuringthe channel resistance of suspended graphene membrane 125, which is usedas a reference resistance R_(ref). This reference resistance R_(ref) isdetermined by placing a control voltage across the sense electrodes 132and 133 and measuring the resistance between the sense electrodes 132and 133. Referring to FIG. 2B, a next step comprises placing thepressure sensor device 100 in a test ambient having an unknown pressureP_(test), and then measuring the channel resistance of suspendedgraphene membrane 125, which is used as a test resistance R_(test). Thistest resistance R_(test) is determined by placing the same controlvoltage across the sense electrodes 132 and 133 and measuring theresistance between the sense electrodes 132 and 133.

Once the reference R_(ref) and test R_(test) resistances are determined,the pressure of the test ambient P_(test) can be determined by thefollowing equation:|R _(test) −R _(ref) |=α|P _(test) −P _(ref)|  Equ. (1)

-   wherein the value α represents the piezo-resistivity factor. In this    mode of operation, the different forces of the applied pressure    causes the suspended graphene membrane to deflect and stretch to    different degrees, which cause changes in resistance of the thin    suspended graphene membrane 125.

The use of graphene as an active electro-mechanical membrane of thepressure sensor device 100 discussed herein is advantageous for variousreasons. For example, graphene is known to have a breaking strength 200times greater than steel. In this regard, an active graphene membrane(e.g., the suspended graphene membrane 125) can be made very thin, downto one atomic layer. Moreover, with an extremely thin and strong activegraphene membrane, the pressure sensor can operate with highersensitivity as compared to an active Si membrane.

In another mode of operation, the optional control cell 210 can be usedas a control measure to eliminate any measured change of resistance ofthe suspended graphene membrane 125 that is caused by chemical doping ofa test gas. In particular, in the exemplary method discussed above, whenthe ambient changes from the reference ambient to the test ambient (testgas), the test gas can chemic ally dope the suspended graphene membrane125, which adds to the change in resistance in addition to the change inresistance caused by the stretching/deflection of the suspended graphenemembrane 125 due to the test ambient pressure. In this regard, thecontrol cell 210 can be used to determine the change in resistance ofthe graphene membrane due to chemical doping and eliminate this factor.

More specifically, referring to FIGS. 2A and 2B, when the referenceambient and test ambient is applied to the pressure sensor device 100,in addition to measuring the channel resistance of the suspendedgraphene membrane 125, the channel resistance of the supported graphenemembrane 120 in the control cell 210 is also measured. The change inresistance ΔR_(ctr) of the supported graphene membrane 120 in thecontrol cell 210 represents the change in resistance due to chemicaldoping of the supported graphene membrane 120 (which is the same orsimilar to the change in resistance due to chemical doping of thesuspended graphene membrane 125). On the other hand, the change inresistance ΔR_(Dev) of the suspended graphene membrane 125 in the devicecell 200 is due to both the chemical doping and the pressure change. Inthis regard, the resistance caused by the change in pressure in thedevice cell 200 can be determined by ΔR_(pressure)=ΔR_(Dev)−ΔR_(ctr).After each test, the chemical doping of the graphene membranes 120 and125 can be removed using known techniques.

FIGS. 3A, 3B, 3C, 3D, 3E, 3F, and 3G schematically illustrate a methodfor constructing a semiconductor nano pressure sensor device accordingto an exemplary embodiment of the invention. In particular, FIGS. 3A,3B, 3C, 3D, 3E, 3F, and 3G are cross-sectional views of thesemiconductor pressure sensor device 100 of FIGS. 1A, 1B, and 1C atvarious stages of fabrication. Referring initially to FIG. 3A, across-sectional view is shown of the semiconductor nano device 100 at aninitial stage of fabrication after forming an insulating layer 110 on asemiconductor substrate 105. In particular, FIG. 3A illustrates aninitial stage of fabrication wherein the device 100 comprises asemiconductor substrate 105 and an insulating layer 100 formed on top ofthe substrate 105. In one exemplary embodiment of the invention, thesubstrate 105 can be a silicon substrate, or a substrate formed with anyother type of substrate material, or multiple layers of substratematerials, commonly used in VLSI fabrication methods.

The insulating layer 110 may be formed using various types of dielectricor insulating materials such as oxides and nitrides, which are commonlyused in VLSI fabrication including, but not limited to silicon nitride,silicon oxide, hafnium oxide, zirconium oxide, aluminum oxide, aluminumnitride, boron nitride or a combination of such materials. Theinsulating layer 110 may be formed using known deposition techniques.The insulating layer 110 may be a nitride layer or an oxide layer thatis formed by growing oxide on silicon using well-known semiconductorfabrication techniques. For example, the insulating layer 110 may beformed of silicon nitride, silicon oxide, hafnium oxide, zirconiumoxide, aluminum oxide, aluminum nitride, or boron nitride or acombination thereof. In a preferred embodiment, the insulating layer 110has a thickness of about 90 nm or about 280 nm (or any suitablethickness to provide sufficient contrast for photolithographic etchingof features on top of the insulating layer 110, as is understood bythose of ordinary skill in the art).

FIG. 3B is a cross-sectional view of the structure of FIG. 3A afteretching a cavity 115 in the insulating layer 110. With this process, anetch mask material is deposited over the insulating layer 110 and thenpatterned to form an etch mask 300 having an opening 302, which servesto define a recessed cavity to be subsequently etched in the insulatinglayer 110. The etch mask 300 may be photoresist mask that is formedusing known photolithographic methods. After forming the etch mask 300,an etching process is performed to etch the portions of the insulatinglayer 110 exposed through the opening 302 in the etch mask 300 to formthe recessed cavity 115 in the insulating layer 110. In one exemplaryembodiment, an anisotropic dry etch process, such as RIE (reactive ionetching) may be used to etch the exposed portion of the insulating layer110 that is exposed through the opening 302 of the etch mask 300 to formthe cavity 115. The etching techniques and environments used to etch theinsulating layer 110 will vary depending on what materials are used toform the insulating layer 110. As noted above, in one preferredembodiment, the cavity 125 may be formed having a width “W” in a rangeof about 0.2 um to about 5.0 um, or more preferably, a range of about0.5 um to about 2.0 um, and etched to a depth “D” in a range of about 20nm to about 300 nm.

FIG. 3C is a cross-sectional view of the structure of FIG. 3B afterforming a graphene layer 310 over the insulating layer 110 and forming asecond etch mask 320 over the graphene layer 310. In one preferredembodiment, the graphene layer 310 is formed on a separate substrate andtransferred onto the surface of the insulating layer 110 using any knowntechnique that is suitable for the given application. For instance, inone standard method, a thin graphene film can be grown by chemical vapordeposition on copper foil. Then a thin film of poly(methyl methacrylate)(PMMA) is spun onto the graphene surface. Then the PMMA/graphene/copperstack is soaked in a copper etchant to remove copper. The PMMA/graphenefilm can then be transferred to the target substrate. The PMMA can thenbe removed by using acetone. The result of this process is the formationof the graphene layer 310 on the surface of the insulating layer 110,whereby the graphene layer 310 will sufficiently adhere to theplanarized surface via Van der Waals interaction forces. In a preferredembodiment of the invention, the graphene layer 310 has a thickness in arange of about one atomic layer to about ten atomic layers.

After forming the graphene layer 310, the etch mask 320 is formed bydepositing an etch mask material over the graphene layer 310 andpatterning the etch mask material to form the etch mask 320 pattern. Theetch mask 320 may be a photoresist mask that is formed using knownphotolithographic methods. The etch mask 220 is patterned to exposeregions of the graphene layer 310 to be etched away, while coveringregions of the graphene layer 310 that define the supported andsuspended graphene membranes.

FIG. 3D is a cross-sectional view of the structure of FIG. 3C afteretching the graphene layer 310 using the etching mask 320 to form thesupported graphene membrane 120 and the suspended graphene membrane 125.The supported graphene membrane 120 is disposed entirely on the surfaceof the insulating layer 110, whereas the suspended graphene membrane 125is disposed over the recessed cavity 115 region such that a portion ofthe suspend graphene membrane 125 is suspended over the cavity 115 andthe peripheral regions of the suspended graphene membrane contact aportion of the insulating layer 110 surface surrounding around theperiphery of the recessed cavity 115. The graphene layer 310 may beetched using any suitable known method, such as using an oxygen plasma.After etching the graphene layer 310, the etch mask 320 is removed,resulting in the structure depicted in FIG. 3D.

A next step in the fabrication process is to form the sense electrodes130, 131, 132, and 133 as shown in FIG. 1B, for example. This processbegins by depositing one or more layers of conductive material over thestructure of FIG. 3D and etching the conducive layer(s) to form theelectrodes. In particular, FIG. 3E is a cross-sectional view of thestructure of FIG. 3D after forming a layer of conductive material 330over the graphene membranes 120 and 125 and the insulating layer 110,and forming an etch mask 340 to define the sense electrodes. FIG. 3F isa cross-sectional view of the structure of FIG. 3E after etching theexposed portions of the layer of conductive material 330 using the etchmask 340 down to the insulating layer 110 to form the sense electrodes130, 131, 132, 133.

The sense electrodes can be formed of conductive materials including,but not limited to, titanium, palladium, gold, aluminum, poly silicon,TiN, TaN, tungsten, or a stack of one or more of such materials. Forinstance, the conductive layer 330 in FIG. 3E can be formed of multiplelayers by sequentially depositing a first seed layer of Ti (about 1 nmthick), a second layer of Pd (about 20-30 nm thick) and a third layer ofgold. The seed layer is formed of Ti or any suitable material that hasgood adhesion on the graphene membranes 120 and 125 and insulating layer110. The second layer is formed of any suitable material such as Pd thatserves to match the work function of the graphene membranes 120 and 125.Preferably, the overall thickness of the sense electrodes 130˜133 is ina range of about 20 nm to about 500 nm. The material layers forming thesense electrodes 130˜133 may be deposited by using known techniques,such as e-beam, sputtering, chemical vapor deposition, etc., thenpatterned by a reactive ion etch (RIE) process or a “lift-off” process.

A next step in the fabrication process is to form the sealing rings 140and 145 to seal the outer peripheral regions of the sense electrodes130, 131, 132, 133 and the graphene membranes 120 and 125, as discussedabove with reference to FIG. 1A, for example. This process is generallyperformed by depositing a layer of sealing material over the structureof FIG. 3F and patterning the layer of sealing material by a RIEprocess, a wet etch process, or a “lift-off” process, to form thesealing rings 140 and 145. In particular, FIG. 3G is a cross-sectionalview of the structure of FIG. 3F after depositing a blanket layer ofsealing material 340 and forming an etch mask 350 that defines thesealing rings. The layer of sealing material 340 may be formed of anysuitable material, such as a spin-on glass material layer, hermetic sealmaterial, or a rubber material, etc., and deposited using knowntechniques suitable for depositing such material. The sealing rings 140and 145 shown in FIG. 1A, for example, are formed by etching away thoseportions of the layer of sealing material 340 exposed by the etch mask350. FIG. 1B is a cross-sectional view of the resulting structure afteretching the layer sealing material 340 and removing the etch mask 350 asshown in FIG. 3G.

It is to be understood that the invention is not limited to theparticular materials, features, and processing steps shown and describedherein. Modifications to the illustrative embodiments will becomeapparent to those of ordinary skill in the art. It should also beunderstood that the various layers and/or regions shown in theaccompanying figures are not drawn to scale, and that one or moresemiconductor layers and/or regions of a type commonly used in suchintegrated circuits may not be explicitly shown in a given figure forease of explanation. Particularly with respect to processing steps, itis to be emphasized that the descriptions provided herein are notintended to encompass all of the processing steps that may be requiredto form a functional integrated semiconductor nano-device. Rather,certain processing steps that are commonly used in forming semiconductordevices, such as, for example, wet cleaning and annealing steps, arepurposefully not described herein for economy of description. However,one of ordinary skill in the art will readily recognize those processingsteps omitted from these generalized descriptions.

Although exemplary embodiments of the present invention have beendescribed herein with reference to the accompanying figures, it is to beunderstood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may bemade therein by one skilled in the art without departing from the scopeof the appended claims.

What is claimed is:
 1. A method of forming a semiconductor pressuresensor device, comprising: forming an insulating layer on asemiconductor substrate; forming a recessed cavity in the insulatinglayer; forming a suspended graphene membrane on the insulating layercompletely covering the recessed cavity, wherein the suspended graphenemembrane has a thickness in a range of about one atomic layer to aboutten atomic layers; forming a first sense electrode and a second senseelectrode on the insulating layer on opposing sides of, and in contactwith, the suspended graphene membrane; forming a sealing ring aroundouter sidewalls of the first and second sense electrodes and thesuspended graphene membrane forming a supported graphene membrane on theinsulating layer in a region adjacent to the first graphene membrane,wherein the supported graphene membrane is physically separate from thesuspended graphene membrane, and wherein an entire surface area on oneside of the supported graphene membrane is in direct contact with theinsulating layer; forming a third sense electrode and a fourth senseelectrode on the insulating layer on opposing sides of, and in contactwith, the supported graphene membrane; and forming a second sealing ringaround outer sidewalls of the third and fourth sense electrodes and thesupported graphene membrane, wherein the suspended graphene membrane isa part of the semiconductor pressure sensor device that is configured tooperate as a device cell for testing pressure of an ambient gas based ona change of resistance of the suspended graphene membrane caused bypressure applied on the suspended graphene membrane by the ambient gas,and wherein the supported graphene membrane is a part of thesemiconductor pressure sensor device that is configured to operate as acontrol cell for determining an amount of change in resistance of thesuspended graphene membrane due to chemical doping of the suspendedgraphene membrane from the ambient gas.
 2. The method of claim 1,wherein the recessed cavity is filled with air.
 3. The method of claim1, wherein the recessed cavity contains a vacuum.
 4. The method of claim1, wherein the insulating layer comprises silicon nitride, siliconoxide, hafnium oxide, zirconium oxide, aluminum oxide, aluminum nitride,or boron nitride or a combination thereof.
 5. The method of claim 1,wherein a width of the recessed cavity between the first and secondsense electrodes is in a range of about 0.2 um to about 5.0 um.
 6. Themethod of claim 1, wherein a depth of the recessed cavity is in a rangeof about 20 nm to about 300 nm.
 7. The method of claim 1, wherein thesealing ring comprises a spin-on glass layer, a Hermetic seal, or arubber seal.
 8. The method of claim 1, wherein the supported graphenemembrane has a thickness in a range of about one atomic layer to aboutten atomic layers.